(1) Field of the Invention
The present invention is directed to the establishment of a fluid-tight seal between a pair of coaxial tubular members of unequal length and/or between a tubular member and a surface from which it extends. More particularly, this invention relates to apparatus for sealing a nozzle tube to a stub tube and/or to the wall of a nuclear reactor pressure vessel. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
In boiling water nuclear reactors, control rods are driven upwardly through nozzles disposed in the lower portion of the reactor pressure vessel. The "nozzles" are supported by and are longer than stub tubes which are welded to the interior wall of the reactor vessel. Each "nozzle" is sealed to its associated stub tube by means of an annular weld between the "nozzle" and the stub tube upper end.
During the operation of a boiling water reactor, a crack may develop in a stub tube or in one of the weld zones. Such a crack may permit the leakage of coolant into the annular space about the control rod nozzle. Because of the high pressure within the interior of the reactor vessel, even a very small crack could result in radioactive fluid passing to the exterior of the reactor vessel via this annular space. It is necessary that any such leakage be halted so that the nuclear reactor may continue to operate.
The repair of leaks which occur in the stub tube area of a reactor are complicated by the radioactive environment as well as by the location of the stub tube at the bottom of the reactor vessel generally underneath the reactor core with its fuel assemblies. The initial prior art method of repairing a failed stub tube member involves removing some or all of the reactor fuel assemblies, completely draining the coolant from reactor vessel and then either replacing or repairing the stub tube member This is an expensive and time consuming procedure.
In U.S. Pat. No. 4,480,841 entitled "Apparatus and Method for Sealing a Tube Joint", which is assigned to the assignee of the present invention, a mechanism for establishing a seal about the welded joint between a tube stub and a "nozzle" is disclosed. This mechanism allows for remote repair of a failed joint. In the apparatus of U.S. Pat. No. 4,480,841, a sleeve fits closely over the joint. A housing surrounds the sleeve and a thrust ring acts to compress packing rings against the sleeve and both the tube stub and nozzle to form a fluid tight seal around the joint. A sealing nut is employed to maintain the compression of the packing seals. The apparatus and method of U.S. Pat. No. 4,480,841 is designed to rectify cracks which occur in the area of the weld which forms the joint between the stub tube and the nozzle tube. However, cracks may form in the stub tube below the bond to the nozzle and in the region where the stub tube is welded to the vessel. The prior art has not addressed the problem of expediciously repairing cracks which occur below the joint between the stub tube and its associated control rod nozzle.